Well spotted, and good to ask.
But, Nope. You're good. Nothing missing. Nothing in the cyclepedia image, or on my LIKE200i.
They were going to put a cup holder down there for Americans, but .....
This engine is probably used in other scooters and fishing boats....so something else might go in there.
See that golden M8 bolt to the left in the pic? - one of those would probably screw in there so you don't lose points at the Pebble Beach Concours d'Elegance.
BTW - that plastic cap covers the port where you look to get the timing mark for setting the valves. The label tells the oil capacity for engine oil changes.
Stig